Photoflash lamp and multiple flashlamp system

ABSTRACT

An improved combustible photoflash lamp is described which produces an increased peak and integrated lumen output per unit lamp volume, and an improved color temperature of light output. The combustible comprises shredded foil substantially comprised of hafnium metal which is burned in a super pressure oxygen atmosphere. The shredded foil cross-sectional area can be varied to further vary the color temperature of the light output. The lamp envelope including the protective lacquer coating on the exterior thereof is substantially transmissive of all visible radiations generated upon operation of the lamp. This lamp eliminates the need for a light-absorbing, color-correcting blue lacquer coating in order to achieve a high color temperature of light output. The lamp is conveniently utilized in an improved multiple flashlamp system.

United States Patent Gulbrasen et al.

[ 51 July4, 1972 East Pittsburgh, all of Pa.; Bruce T. Buzalski, Dover, NJ.

Westinghouse Electric Corporation, Pittsburgh, Pa.

[22] Filed: June 15,1970

[21] Appl.No.: 46,378

[73] Assignee:

Nijland et a1. ..431/95 3,303,674 2/1967 Anderson ....431/94 X 3,304,750 2/1967 Anderson ..431/94 3,377,126 4/1968 Nijland et al.. .....431/94 3,392,273 7/1968 Fink et a1 ....240/1.3 3,490,855 l/l970 Buzalski ..431/95 Primary ExaminerLouis .lQCapozi Attorney-A. T. Stratton, W. D. Palmer and W. G. Sutcliff [5 7] ABSTRACT An improved combustible photoflash lamp is described which produces an increased peak and integrated lumen output per unit lamp volume, and an improved color temperature of light output. The combustible comprises shredded foil substantially comprised of hafnium metal which is burned in a super pressure oxygen atmosphere. The shredded foil cross-sectional area can be varied to further vary the color temperature of the light output. The lamp envelope including the protective lacquer coating on the exterior thereof is substantially transmissive of all visible radiations generated upon operation of the lamp. This lamp eliminates the need for a light-absorbing, color-correcting blue lacquer coating in order to achieve a high color temperature of light output. The lamp is conveniently utilized in an improved multiple flashlamp system.

11 Claims, 3 Drawing Figures PHOTOFLASH LAMP AND MULTIPLE FLASHLAMP SYSTEM BACKGROUND OF THE INVENTION The zirconium shredded foil, super-oxygen pressure photoflash lamp has had a significant impact upon the use of flashlamps in picture taking. The reduction in lamp size while still providing adequate light output has made the use of flashlamps more convenient. The multiple flashlamp system using such lamps has had a further impact upon the amateur photography market.

The zirconium shredded foil photoflash lamp provides light output with a color temperature at peak lumen output of about 4,200 Kelvin. In order to make such lamps more readily usable with so-called outdoor color films, a light-absorptive blue filter is provided which absorbs a higher proportion of the longer wavelengths of the visible light than of the shorter wavelengths and thus increases the color temperature of the light output. The color temperature of light output of the standard zirconium shredded foil lamp is about 4,200 Kelvin. With a light-absorptive, blue lacquer coating the color temperature of the light output is shifted to about 5,000 Kelvin or higher.

The use of hafnium metal as a photoflash lamp combustible is suggested in U.S. Pat. No. 3,303,674, for use with a lamp designed for focal plane camera systems. The lamps described therein had a relatively low peak lumen output and a long duration of light output. It is well known in the art that by increasing the cross sectional dimension of the shredded foil combustible material one delays the rise time to peak lumen output upon combustion.

SUMMARY OF THE INVENTION The photoflash lamp comprises a hermetically sealed light transmissive envelope, with ignition means adapted to be activated to initiate combustion, a predetermined oxygen at- .color temperature of the light output at peak lumen output is at least greater than about 4,600 Kelvin.

The lamp of the present invention produces a substantially increased peak lumen output which is approximately about 0.6 megalumens per cubic centimeter of lamp volume. Some measure of control of the color temperature of the light produced is effected by varying the cross sectional area of the combustible shredded foil from approximately 1.2 X square inch to 1.9 X 10 square inch to efiect a color temperature change of from 4,600 to 5,000 Kelvin.

The lamp of the present invention can also be advantageously utilized in multiple flashlamp systems. The lamp when used as an individual lamp or as a component of a multiple flashlamp system eliminates the need for the conventional light absorptive, blue lacquer, color correction coating which is currently used on lamps designed for use with outdoor color film. The quality of the light produced by a lamp of the present invention is thus comparable, and substitutable for a blue color corrected prior art lamp, but with a significantly increased total light output.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged elevational view of a photoflash lamp embodiment of the present invention;

FIG. 2 is a perspective view of a multiple flashlamp system,

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention can thus be described by reference to the exemplary embodiments as shown in FIG. 1 and FIG. 2. In FIG. 1, the photoflash lamp 10 comprises a hermetically sealed, light transmissive glass envelope 12, ignition means comprising an electrically conductive filament 18, for example formed of tungsten. A readily combustible conventional primer 20, such as a mixture of powdered zirconium and potassium perchlorate is deposited on filament 18, or on the ends of leadins 14 and 16 proximate segments of the filament 18. Electrically conductive lead-ins l4 and 16 are sealed through the envelope and electrically connected to the ignition filament 18. A clear lacquer coating 24 is disposed on the exterior of the envelope 12. The primary combustible material is a shredded foil 22, which substantially comprises hafnium metal. For a flashlamp with a volume of about 0.6 cubic centimeter, the shredded foil substantially comprising hafnium is included in an amount of about 44 milligrams, which is about 4 X 10 gram-atom per cubic centimeter of lamp volume. The lamp is tipped off with an oxygen fill of about 8 atmospheres. The glass envelope 12 and the conventional clear lacquer coating 24 thereon, are substantially transmissive of all visible radiations produced upon ignition of the lamp. The lacquer is typically cellulose acetate lacquer, which is more fully described in U.S. Pat. No. 3,022,653, issued Feb. 27, 1962.

It has been discovered that the quality of the light output as denoted by the term color temperature can be determined to some extent by varying cross-sectional dimension of the shredded foil combustible. For example, in the 0.6 cubic centimeter volume lamp described above, when the shredded foil was constructed of 0.0009 inch thick foil which was 0.0013 inch wide, thus yielding a cross-sectional area for the shreds of 1.2 X 10' square inch, the color temperature of the light output was approximately 4,600K. When the shredded foil width was increased to 0.0021 inch wide, and the cross-sectional area of the shred approximately 1.9 X10 square inch, the color temperature of the light output was increased to about 5,000 Kelvin.

The hafnium foil used in the lamps described herein is typically reactor grade metal, which contains about 3 weight percent zirconium. Lamps have been prepared with combustible containing an increased weight percent of zirconium. With increased zirconium content the color temperature is decreased and the light output peak is diminished. Combustible with up to about percent hafnium 10 percent zirconium by weight still produce an improved color temperature and light output characteristic. The cross-sectional area of the foil has an effect on the color temperature of light output, with in general the greater the cross-sectional area the higher the color temperature.

In FIG. 2 there is shown a disposable multi-photoflash lamp unit or so-called flashcube 30 which is another use for the lamps of the present invention. The lamp unit 30 comprises a generally cubical light-transmissive plastic cover or enclosure 32, which is fitted over four reflector components 34 and a corresponding number of photoflash lamps 36. The photoflash lamps 36 of generally similar construction are more completely shown in FIG. I. The enclosure 12 is seated against a plastic base member 38. A flashcube structure of this type is more fully described in U.S. Pat. No. 3,244,087 issued Apr. 5, 1966. The plastic cover or enclosure 32 is a polystyrene which is substantially transmissive of all visible radiations. In order to attain a high color temperature for the light output the prior art practice has been to use a blue lacquer coating on the individual lamps, or to provide a blue plastic cover as plastic cover 32.

Color temperature is a term used to describe the color of a light source by comparing it with the color of a black body. Color temperature is not a measure of actual temperature, but merely indicates spectral distribution, with the assumption that the light source closely resembles a black body in color. There is no generally accepted method for assigning a color temperature value to the light output of a photoflash lamp. In

determining color temperatures as described herein, for the light output of the lamps of the present invention, there is measured the ratio of intensities of emitted light at two wavelengths e.g. 411 and 560 nanometers using phototubes. As a control standard, this same ratio of wavelengths was measured for conventional zirconium foil filled flashlamps and the zirconium foil flashlamp is generally accepted as producing radiations having a color temperature of 4,200 K.

The phototubes used in this determination of color temperature were lP39 tubes with narrow band-pass interference wherein C has a constant value of 1.43879 1 0.00006 cmdeg, and A and A, are wavelengths at which the ratios r and r were taken. The ratio r is of the black body emittance for the sample for which the color temperature T is to be determined, and the ratio r is of the black body emittance for a standard source exhibiting a color temperature T L Thus, by determining experimentally the emittance ratio at A 411 nm, and A, 560 nm, for a zirconium flashlamp with a color temperature of light output of. about 4,200 Kelvin, and by measuring this same ratio for the flashlamps of the present invention, it is possible to determine the color temperature of light output for these lamps.

It must be understood that this method of measuring color temperatures assumes that the spectral distribution of light produced by the burning of molten metal-metal oxide substantially comprising hafnium will be sufficiently similar to a zirconium-zirconium oxide system. It is also assumed that a color temperature of 4,200 K. for the zirconium lamp will form the basis of an accurate determination for color temperatures for the present lamps. These assumptions and their reliability are supported by a comparison of 'color film response when used with the present lamp, compared to use with a clear lacquered zirconium lamp. The color film response to the present hafnium lamps is comparable to the response using a high color temperature blue lacquer coated zirconium lamp.

It should also be understood that when referring to zirconium flashlamps as producing light with a color temperature of about 4,200 Kelvin, this is an average value for a large sampling of lamps. The measured values of color temperature for such lamps will vary over a range of 150 K. from this 4,200 K. average value. The same range of variations are observed for lamps of the present invention, and when reciting a color temperature range of 4,600 to 5,000 Kelvin for these lamps, these are average values, with the measured ranges being approximately 150 Kelvin from these average values.

The lumen output data for lamps of the present invention are compared to prior art zirconium shredded foil lamps operated in the multiple lamp system shown in FIG. 2, and the results shown in FIG. 3. Curve A is a plot of the zonal lumens generated by a lamp of the present invention plotted against milliseconds, for the 0.6 cubic centimeter lamp embodiment of the present invention. The lamp produces the peak lumen output of about 60,000 zonal lumens which is about 0.1 peak zonal megalumens per cubic centimeter of lamp volume.

Curve B plots this same relationship for the light output of a 0.6 cubic centimeter zirconium shredded foil lamp. Curve C is a plot of the zonal lumen second output for the hafnium lamp embodiment described above plotted against milliseconds. It can be seen that at about 25 milliseconds, about 650 zonal lumens are produced. Curve C can be compared with Curve D which represents the zonal lumen second output for the same size zirconium foil lamp. Curve A is a plot of the zonal lumen output for a hafnium foil lamp of the present invention wherein the foil was about 0.0009 inch thick and about 0.0013 inch wide. Curve C is a plot of zonal lumen seconds for this same lamp. It is apparent from these curves that the use of a narrower cut of foil results in a faster time to peak, an increased peak lumen value, and a faster rise to a high lumen second value. I

The light output curvedescribed in FIG. 3 refers to zonal lumens and zonal lumen seconds. The term zonal lumens as used in this description means the lumen values over a square filed formed by a 40 angle field projected in both the vertical and horizontal planes extending out from the lamp. The zonal lumen values given were measured using the multiple flashlamp system shown in FIG. 2. While the absolute values given will be only significant for this system, the relative performances of the lamps of the present invention compared to the prior art lamps clearly shows the advantages of the present lamps. Y

The invention has been described by reference to a particular lamp size and fill parameters, but is not limited to this embodiment. It is apparent that larger and smaller photoflash lamp embodiments can be prepared. For example, in another embodiment of the invention the glass envelope is what is termed an M-2 bulb size, with a volume of approximately 5 cc. The combustible foil substantially comprising hafnium is included in an amount of about 88 mg. and the oxygen pressure is approximately 1.6 atmosphere.

We claim as our invention:

1. A photoflash lamp comprising a hermetically sealed lighttransmissive envelope having a protective coating thereon, ignition means within said envelope adapted to be activated to initiate combustion, a combustion-supporting atmosphere substantially comprising oxygen at a predetermined pressure enclosed by said envelope, and a predetermined amount of shredded combustible foil substantially comprising hafnium enclosed by said envelope, said lamp envelope and its protective coating being substantially transmissive of visible radiations, and said lamp on being flashed producing light output having a color temperature at maximum output at least greater than about 4,600 K.

2. The lamp as specified in claim 1 wherein; said combustible foil consists essentially of hafnium that contains about three percent by weight of zirconium, and the color temperature of the light output is varied from about 4,600 to 5,000" K by varying the cross-sectional area of said shredded foil from approximately 1.2 X 10' square inch to 1.9 X 10' square inch.

3. The lamp as specified in claim 1 wherein; said envelope has a volume less than one cubic centimeter, said combustible shredded foil is present in an amount of about 4 X 10" gramatom per cubic centimeter of lamp volume, and said oxygen atmosphere is about 8 atmospheres pressure, with the peak lumen output being about 0.6 megalumens per cubic centimeter of lamp volume.

4. Thelamp as specified in claim 1 wherein said combustible shredded foil contains up to about 10 weight percent zirconium.

5. In a multiple-flashlamp system comprising a plurality of flashlamps, an integral reflector about each lamp, and a plastic enclosure structure about said lamps, the improvement comprising a hermetically sealed envelope which is substantially transmissive of visible radiations, ignition means to initiate combustion, a predetermined oxygen atmosphere, and combustible shredded foil substantially comprising hafnium, with said plastic enclosure structure being substantially transmissive of visible radiations, and the light output from said system upon flashing of an individual lamp having a color temperature, at the time of peak lumen output, which is at least greater than about 4,600 K. v

6. The improvement set forth in claim 5 wherein; said envelope has a volume of about 0.6 cubic centimeter, said combustible shredded foil is present in an amount of about 4 X gram-atom per cubic centimeter of lamp volume, and said oxygen atmosphere is about eight atmospheres, to produce light output with an average value of about 650 zonal lumen seconds in 25 milliseconds, with a peak lumen output of about 0.] peak zonal megalumens per cubic centimeter of lamp volume.

7. In a photoflash lamp, the combination of;

a sealed glass envelope that has a protective coating of clear plastic thereon and contains oxygen at super-atmospheric pressure,

a combustible material within said envelope consisting essentially of reactor grade hafnium foil in shredded form, and

means for igniting said shredded hafnium foil,

the thickness and width of the hafnium foil shreds being so correlated that the lamp, when ignited, produces a flash of light that has a color temperature of at least about 8. The combination of claim 7 wherein;

said envelope has a volume less than 5 cubic centimeters and contains several atmospheres of oxygen, and

the cross-sectional area of the hafnium foil shreds is within a range of approximately 1.2 X 10 to 1.9 X 10" square inch.

9. The combination of claim 8 wherein;

said envelope has a volume of about 0.6 cubic centimeter and contains about 8 atmospheres of oxygen, and

the hafnium foil shreds are about 0.0009 inch thick and from about 0.0013 to 0.0021 inch wide.

10. The combination of claim 9 wherein;

said envelope contains about 44 milligrams of shredded hafnium foil, and

the hafnium foil shreds have a thickness of about 0.0009

inch and a width of about 0.0013.

1 l. The combination of claim 9 wherein;

said envelope contains about 44 milligrams of shredded hafnium foil, and

the hafnium foil shreds have a thickness of about 0.0009

inch and a width of about 0.0021 inch. 

2. The lamp as specified in claim 1 wherein; said combustible foil consists essentially of hafnium that contains about three percent by weight of zirconium, and the color temperature of the light output is varied from about 4,600* to 5,000* K by varying the cross-sectional area of said shredded foil from approximately 1.2 X 10 6 square inch to 1.9 X 10 6 square inch.
 3. The lamp as specified in claim 1 wherein; said envelope has a volume less than one cubic centimeter, said combustible shredded foil is present in an amount of about 4 X 10 4 gram-atom per cubic centimeter of lamp volume, and said oxygen atmosphere is about 8 atmospheres pressure, with the peak lumen output being about 0.6 megalumens per cubic centimeter of lamp volume.
 4. The lamp as specified in claim 1 wherein said combustible shredded foil contains up to about 10 weight percent zirconium.
 5. In a multiple-flashlamp system comprising a plurality of flashlamps, an integral reflector about each lamp, and a plastic enclosure structure about said lamps, the improvement comprising a hermetically sealed envelope which is substantially transmissive of visible radiations, ignition means to initiate combustion, a predetermined oxygen atmosphere, and combustible shredded foil substantially comprising hafnium, with said plastic enclosure structure being substantially transmissive of visible radiations, and the light output from said system upon flashing of an individual lamp having a color temperature, at the time of peak lumen output, which is at least greater than about 4,600* K.
 6. The improvement set forth in claim 5 wherein; said envelope has a volume of about 0.6 cubic centimeter, said combustible shredded foil is present in an amount of about 4 X 10 4 gram-atom per cubic centimeter of lamp volume, and said oxygen atmosphere is about eight atmospheres, to produce light output with an average value of about 650 zonal lumen seconds in 25 milliseconds, with a peak lumen output of about 0.1 peak zonal megalumens per cubic centimeter of lamp volume.
 7. In a photoflash lamp, the combination of; a sealed glass envelope that has a protective coating of clear plastic thereon and contains oxygen at super-atmospheric pressure, a combustible material within said envelope consisting essentially of reactor grade hafnium foil in shredded form, and means for igniting said shredded hafnium foil, the thickness and width of the hafnium foil shreds being so correlated that the lamp, when ignited, produces a flash of light that has a color temperature of at least about 4,600* K.
 8. The combination of claim 7 wherein; said envelope Has a volume less than 5 cubic centimeters and contains several atmospheres of oxygen, and the cross-sectional area of the hafnium foil shreds is within a range of approximately 1.2 X 10 6 to 1.9 X 10 6 square inch.
 9. The combination of claim 8 wherein; said envelope has a volume of about 0.6 cubic centimeter and contains about 8 atmospheres of oxygen, and the hafnium foil shreds are about 0.0009 inch thick and from about 0.0013 to 0.0021 inch wide.
 10. The combination of claim 9 wherein; said envelope contains about 44 milligrams of shredded hafnium foil, and the hafnium foil shreds have a thickness of about 0.0009 inch and a width of about 0.0013.
 11. The combination of claim 9 wherein; said envelope contains about 44 milligrams of shredded hafnium foil, and the hafnium foil shreds have a thickness of about 0.0009 inch and a width of about 0.0021 inch. 